Its members aren’t just from her high school. More than 3.3 million people, the majority 13- to 22-year-olds, used the site in June, according to comScore Media Metrix. It ranks below MySpace, which had 70.5 million visitors, and Facebook, which had 28 million visitors, but is on par with many of the other social-networking sites trying to carve out an audience and become a destination for at least some of the time people are spending online.